The spell if I read it correctly is instantaneous, so it would mean it has to be 'housed' for a while in another body still while hers gets healed (with magic should take just a little bit)
Remember also even if Jaine is healed and has the baby we just have a healthy pregnant, unmarried Queen. Though for any case where she keeps the kid it's not a bad idea, since it lessens the risk to her --though as stated before with all the transfers and the actual birth to go through the baby has more chances of problems--
But definitely something worth bringing up.